You have to use a reverse ring adapter to fit in the tubes. I tested it out by holding it in front of the tubes and it wasnt an easy feat, I had to really squeeze my eyes to focus and I wish I had a larger viewfinder. I compared between result from lens + tubes and reversed lens with tubes and the magnification with reversed lens is higher but I think you loose the DOF and camera shake is at 7 richter scale magnitude.
Overall, macro photography is tough. Be aware of the constraints if you are into this DIY macro because my neck is a bit aching from looking down, closing in the subject all the time, having eye strain from too many eye squeezing and lastly the weight strain of the camera unless you are using tripod, then thats no problem.
Here are the test results: